1. Field of the Invention
The present invention relates to an apparatus for attaching the self-piercing nuts to one side of a panel (viz. metal plate), wherein each nut driven by a punch has an end face to cooperate with a piercing-caulking die located on the other side of the panel and in alignment with the nut, such that the end face is forced to bite the panel to form therein a hole, whose brim is simultaneously caulked to plastically deform and become integral with the nut.
2. Prior Art
The self-piercing nuts capable of being secured to a metal plate when or during the latter is pressed have been and are used more and more in the mass production of metal plate products as in the automobile industry.
Each of the apparatuses for attaching to a panel the self-piercing nuts usually comprises a punch located on one side of the panel and striking the nuts towards the panel. Each apparatus comprises also a piercing-caulking die facing the punch and located on the other side of the panel. Such an apparatus further comprises a guide member through which the punch slidably reciprocates, and a nut holder having a path extending perpendicular to the guide member and terminating as an end aperture so as to feed the nuts. In many cases, those apparatuses are incorporated in a pressing machine together with other pressing dies or tools. The nuts are not necessarily fixed only to a plane portion of a metal panel, but often fixed to bottoms defining the bent or drawn portions of an L-shape or U-shape.
Typically, the prior art apparatuses for fixing the self-piercing nuts onto a metallic panel are constructed in such a manner as disclosed for example in the Japanese Utility Model Publication No. 63-20512. This apparatus comprises a nut holder capable of sliding along and relative to a punch for striking each nut. The nut holder has a guide post secured thereto and extending in parallel with the punch. A spring disposed in the guide post always urges the nut holder towards its normal position. The guide post is designed so long as to protect the nut from jamming while sliding along the punch. In consequence, a portion (hereinafter referred to as `punch block`) consisting of the punch and the nut holder in the apparatus must be of such an increased overall height of length that the apparatus is difficult to be installed in a pressing machine having a small `shut height`.
The punch block has to be placed in a hollow space of the metal plate (hereinafter referred to as `workpiece`) that has been pressed into a reversed-L, reversed-U or hat shape. Correspondingly, the piercing-caulking die is located outside the workpiece. However, it is difficult for the prior art punch block to take its operable position in such a narrow space, due to such a large axial dimension. Thus, it has scarcely been possible to secure the self-piercing nuts to an upright wall of the hollow space.